1. Field of the Invention
This invention relates to a method for reproducing a high quality image from an image which was recorded with an incorrect exposure on a color photosensitive material.
2. Description of the Prior Art
There have heretofore been used systems wherein various images are recorded on a sheet of color photographic film accommodated in a camera and the color photographic film on which the images have been recorded is then subjected to development processing. Thereafter, in a printing apparatus, light is irradiated to the color photographic film, and light which has passed therethrough is irradiated to sheets of photographic paper on which images are reproduced.
In the aforesaid systems, it often occurs that, when an image is recorded on photographic film which is accommodated in a camera, the exposure set in the camera is unsuitable for the photographic film. Specifically, the photographic film is often exposed to an insufficient amount of light (this state is referred to as underexposure) or to an excessive amount of light (this state is referred to as over-exposure).
FIG. 1 is a graph showing some examples of characteristic curves of photographic film. In FIG. 1, the logarithmic value cf the light amount E to which the photographic film was exposed (hereinafter referred to as log E) is plotted on the horizontal axis. Red, green, and blue spectral densities D, which are determined with a densitometer, are plotted on the vertical axis.
As illustrated in FIG. 1, the photographic film is designed so that, when it is irradiated with an exposure falling within the correct exposure range A, which approximately corresponds to the middle part of the log E axis, an image is formed which has good contrast and good color balance. When the photographic film is underexposed (i.e. when the exposure falls within the range B to the left side of the correct exposure range A) or is overexposed (i.e. when the exposure falls within the range C to the right side of the correct exposure range A), the gamma values which represent the degrees of inclination of the characteristic curves decrease. Also, the gamma values are not constant (i.e. the change of the spectral densities D with respect to log E becomes nonlinear), and the color balance changes. Therefore, in cases where an underexposed image or an overexposed image was recorded on the photographic film in a camera, even if the amount of light irradiated to photographic paper, a filter, or the like is adjusted in the course of printing the image on the photographic paper, a correct image cannot be reproduced on the photographic paper, and an image having undesirably soft gradation and bad color balance is obtained.
In order for a correct image to be reproduced from an incorrectly exposed image, the technique disclosed in, for example, Japanese Unexamined Patent Publication No. 62(1987)-7290 has been suggested. The disclosed technique comprises the steps of scanning an image, which has been recorded on photographic film, with a scanner or the like, in order to obtain three color signals which represent information about three colors and which comprise signal components representing respective picture elements of the image. Thereafter, the mean value, the maximum value, and the minimum value of each color signal are assigned as characteristic values. On the basis of the characteristic values, each color signal is corrected so that the gamma values thereof change. In this manner, the gradation of the image is corrected. When the gamma values are corrected with the disclosed technique and an image is reproduced on photographic paper with a laser printer or the like, a reproduced image having slightly better image quality will be obtained.
However, as described above, when the photographic film is underexposed or overexposed, the gamma values are not constant (i.e. the change of the spectral densities D with respect to log E becomes nonlinear). Therefore, with the disclosed technique, the gamma values cannot be corrected accurately. Also, the values of the three color signals, which are detected with the scanner, vary in accordance with the spectral characteristics of the optical filters used when the three color signals are being detected. Since a laser printer is used to reproduce an image on photographic paper and the characteristics of the optical filters are not associated with the characteristics of the laser printer, a correctly exposed image cannot be reproduced from an incorrectly exposed image with the disclosed technique.